[Chemistry] How do you find the new concentration?

1. The problem statement, all variables and given/known data
For solution A the concentration is 7.00x10^-4 mol/L. You transfer 10ml of the solution A out into a 10 dram vial and add 10mL of 0.1M HCL acid solution, and the new mixture is called solution B. What is the concentration of solution B?

2. Relevant equations3. The attempt at a solution

is this right approach? first find the mol of solution A, and then find the mol of HCl. Add them together and divided by the total volume.